An important life-saving technique for individuals diagnosed with weakened hearts includes mechanically assisting the heart to pump blood. Assistance to the heart ensures an adequate blood pressure for sufficiently supplying blood throughout the body without undue stress on the heart muscle. Typically, a device such as a heart compression apparatus, or cuff, carries out the assistance during invasive surgery. An alternative related application for the apparatus involves cardiopulmonary resuscitation (CPR) techniques to rhythmically squeeze the heart in cases where the heart fails to beat at all.
Those skilled in the art have proposed a variety of devices to successfully carry out the heart compression function to maximize support for the heart and provide reliable and accurate functionality. One such cuff device, disclosed in pending Provisional U.S. patent application Ser. No. 60/028,722, filed on Oct. 18, 1996 and assigned to the assignee of the present invention, carries and supports the heart during invasive surgery while uniformly applying pressure directly to the heart through means of an inflatable liner. The liner is cyclically inflated and deflated by an inflation system to apply pressure to the heart.
Because each heart pumps blood according to a pressure profile unique for each patient, successful cardiac compression on the inflatable liner depends upon the inflation system being controllable to somewhat match the patient's personal cardiac rhythm or pressure profile. An equally important consideration involves the limited duration of the heart's systolic cycle, which provides only about fifty to one-hundred milliseconds within which to establish synchronous compression.
One proposal for pneumatically driving a cardiac compression device, such as an Anstadt cup or intra-aortic balloon, is disclosed in U.S. Pat. No. 4,016,871. The pneumatic drive system is housed within a console and includes a relatively low-pressure compressor coupled in parallel to a pressure regulator and a vacuum regulator. The respective regulators are connected to respective reservoirs having outputs coupled to respective solenoid valves. The solenoid valves are controlled by an electronic sequencer to pass pressurized pulses through an elongated pressure line coupling the console to the cardiac compression device for inflation and deflation thereof.
A second proposal, such as that disclosed in U.S. Pat. No. 5,300,017, describes a driver for a cardiac compression device including an isolator with respective first and second chambers separated by a flexible diaphragm. The first chamber is coupled through respective positive and negative pressure switching valves to respective positive and negative air pressure sources. The second chamber of the isolator communicates directly with the cardiac compression device. The diaphragm responds to positive or negative pressures in the range of about 10 mmHg from the respective sources to decrease or increase the volume within the second chamber, thereby pressurizing or depressurizing the cardiac compression device.
While these proposals appear to work well for their intended applications, they are often disposed several feet from the cardiac compression device. This is typically because of the controlled conditions associated with surgical environments. As a result, the extended length of the pressure line generally requires a relatively large diameter tube to minimize line resistance. The increase in volume, as a consequence, increases the overall flowrate through the system, thereby increasing the component sizes and costs.
What is needed and heretofore previously unavailable is a high-pressure drive system for a cardiac compression device, such as a cuff, that enables reduced component sizes and improved rise-time response. A further need exists for such a system having improved safety features for patient protection. The high-pressure drive system of the present invention satisfies these needs.